1. Field of the Invention
The present invention relates to endoluminal stent graft structures. More particularly, the present invention relates to endoluminal stent grafts for use in a body vessel system that includes a main vessel and a branch vessel emanating from the main vessel.
2. Description of Related Art
A conventional endoluminal stent graft typically includes a radially expandable reinforcement structure, formed from a plurality of annular stent rings, and a cylindrically shaped graft material defining a main body to which the stent rings are coupled. Stent grafts are well known for use in tubular shaped human vascular or other body vessel.
At deployment, after intravascular insertion and transluminal transport, i.e., within the vessel, to the point of use within a damaged or diseased vessel, for example, an aneurysmal artery, a compressed stent graft is radially expanded. A stent graft is self-expandable or expandable by application of pressure applied outwardly to the interior portion of the stent graft. After deployment, the stent graft is fixed in place at the location of initial deployment within the vessel. Complications such as Type I endoleaks can occur if the stent graft migrates after deployment.
One approach in the prior art, used to securely fix the stent graft to the vessel at the point of initial deployment, relied on providing the stent graft with an outward biasing radial force at the contact interface between the stent graft and the interior wall of the vessel in which it was deployed. Typically, a radial force, biasing outwardly from the stent graft toward the interior wall of the vessel, was supplied by a spring element at one or both ends of the stent graft. The spring element urged the stent graft into abutting contact with the interior wall of the vessel where frictional forces between the spring element and the vessel interior wall provided both a liquid-tight seal between the stent graft and the vessel as well as fixation of the stent graft at its location of initial deployment.
In cases where the contact interface, sometimes called the landing zone, between the stent graft and the vessel wall is small, the surface area on the interior of the vessel available for application of outward radial force may be insufficient to firmly and permanently seal and fix the stent graft. An abdominal aortic aneurysm with a short “neck” for a landing zone is an example where the area available for application of radial force might not be enough to seal and fix a stent graft.
Accordingly, in the prior art, stent grafts sometimes included bare springs to extend the length of the stent graft such that the spring element contacted and could be fixed to healthy vessel tissue above or below the area of weakened or damaged vessel tissue.
Illustratively, FIG. 1A shows a partial cutaway view of a vessel system 150, for example an artery system, containing one example of a deployed prior art stent graft 100. Vessel system 150 includes a main vessel 152, for example an aorta, and one or more branch vessels 154 emanating from main vessel 152, such as renal arteries emanating from the aorta. Main vessel 152 includes an aneurysm 156, i.e., a weakened, radially distending vessel segment, caused by disease. Aneurysm 156 is at risk of rupture resulting in, for example, extravasation of blood into the peritoneal cavity or into tissue surrounding diseased main vessel 152.
An evolving method for treating aneurysmal disease of the type depicted in FIG. 1A, is termed “endovascular aneurysmal exclusion”. The goal of endovascular aneurysmal exclusion is to exclude from the interior of aneurysm 156, i.e., an aneurysmal sac 158, all aorta pressurized fluid flow, thereby reducing the risk of rupture of aneurysm 156 requiring invasive surgical intervention.
One procedure developed to accomplish this goal entailed internally spanning affected main vessel 152 with stent graft 100. Prior art stent graft 100 was positioned and deployed within main vessel 152 through a vessel system furcation 159, such as an iliac artery of an artery system, with an insertion stent graft catheter (not shown) by percutaneous or cut-down procedures well know to those of skill in the art. Prior art stent graft 100 typically included a radially expandable cylindrical reinforcement structure, sometimes referred to simply as a stent 104, formed from a plurality of annular stent rings 106 coupled to a biocompatible tubular graft material 102. A bare spring element 108 of prior art stent graft 100 was coupled to the proximal end of stent graft material 102.
Graft material 102 was configured in a tubular shape forming a main body 103 spanning across aneurysm 156. Prior art stent graft 100 was fixed in main vessel 152 by bare spring element 108 which helped established a substantially fluid-tight seal above aneurysm 156 at a graft/vessel interface, sometimes called a landing zone 160. Once deployed, prior art stent graft 100 provided an alternate conduit for fluid flow through main body 103 and, at the same time, excluded fluid flow into aneurysmal sac 158.
In the prior art stent graft 100 of FIG. 1A, graft material 102 did not extend beyond a branch point 162, where branch vessel 154 begins to emanate from main vessel 152, to the end of prior art stent graft 100 at bare spring element 108. If graft material 102 were extended such that it passed by a vessel ostium 166 leading into branch vessel 154 from main vessel 152, graft material 102 would block vessel ostium 166 and cut-off fluid flow into branch vessel 154.
However, graft material 102 forming main body 103 may be advantageously utilized to assist in forming a liquid-tight seal between prior art stent graft 100 and healthy tissue beyond branch point 162 at landing zone 160 at the interior wall of main vessel 152 above diseased or damaged tissue at a neck 164 of aneurysm 156. FIG. 1B shows a close-up, cross-section view of one branch point 162 of vessel system 150 of an embodiment similar to that shown in FIG. 1A containing an example of a deployed prior art stent graft 180 that further includes extended graft material 102E beyond branch point 162.
In FIG. 1B, to address the problem of blocking of vessel ostium 166, extended graft material 102E included a branch opening (aperture) 110. Thus, prior art custom configured stent graft 180 with a side window or fenestration was often referred to as a “fenestrated” stent graft. At deployment, prior art stent graft 180 was main axially and rotationally positioned within main vessel 152 such that branch opening (aperture) 110 aligned with vessel ostium 166 when prior art stent graft 180 was radially expanded. In this configuration, a portion of the fluid flow proceeded from main vessel 152, through branch opening (aperture) 110, through vessel ostium 166, and into branch vessel 154.
It is well known by those of skill in the art that a vessel system 150 is by nature tortuous, asymmetrical and, within limits, individually variable. Thus, when deploying prior art stent graft 180 it was often difficult to position branch opening (aperture) 110, both main axially along main vessel 152 and rotationally about main vessel 152, exactly at vessel ostium 166. Misalignment between branch opening (aperture) 110 in extended graft material 102E and vessel ostium 166 could result in partial or complete blocking of vessel ostium 166 thereby restricting or completely cutting-off fluid flow into branch vessel 154, which is unacceptable. Even when (ring) branch opening (aperture) 110 was substantially aligned with vessel ostium 166 at initial deployment, slight migration of prior art stent graft 180 could cause subsequent misalignment and resultant fluid flow blockage.
However, a rigid ring branch opening (aperture) 110 was branch axially centered along a branch graft central axis Lb that is substantially perpendicular to a main body central axis Lm of main body 152. As noted above, stent grafts were generally compressed in a radial and not axial direction prior to deployment. Also, the axial and rotational alignment difficulties described above continue to be an issue.
Further, branch vessel 154 is often not completely perpendicular to main vessel 152. The branch angle between branch vessel 154 and main vessel 152 often varies from patient to patient given the tortuous and asymmetrical nature of vessels. Accordingly, prior art stent graft 180 containing a rigid (ring) branch opening (aperture) 110 was often custom fabricated, at considerable expense, to accommodate the vessel structure of a particular patient and to attempt to avoid misalignment.
What is needed is a stent graft containing a branch opening (aperture) or graft that is simply configurable into a compressed state prior to deployment. Further, what is needed is a branch opening (aperture) or graft that is easily aligned with, and conforms, without kinking or collapsing, to a tortuous and asymmetrical branch vessel in which it is deployed.